Structure-function relationships in cellular copper control

Abstract

X-ray absorption spectroscopy and computational chemistry have been used to probe the structure of biomolecules involved in cellular copper homeostasis. X-ray absorption spectroscopy shows that copper chaperones involved in cytochrome c oxidase assembly bind Cu(I) with trigonal coordination environments in poly-copper thiolate clusters, but the number of coppers in these clusters remains unclear. X-ray absorption spectroscopy of the metal-sensing transcription factor-1 from Drosophila melanogaster and metallothionein from Saccharomyces cerevisiae with stoichiometries of four or less shows a tetracopper cluster in an all-or-none manner in these molecules. These results suggest that cooperative binding of copper to form tetracopper clusters may be a common mechanism employed by copper control molecules. The active site structure of the novel copper-sensitive repressor CsoR in Mycobacterium tuberculosis binds copper in a trigonal coordination geometry with two sulfur and one nitrogen donors according to X-ray absorption spectroscopy results. Molecular dynamics simulations of both apo- and Cu-bound CsoR reveal local conformational changes in CsoR upon copper binding, which suggests multiple possible mechanisms of Cu-dependent transcriptional regulation by CsoR. Finally, X-ray absorption spectroscopy and X-ray fluorescence imaging have been used to understand the molecular basis of a promisng new treatment for Wilson’s disease (a genetic disorder of Cu homeostasis) using tetrathiomolybdate. Overall, the results presented provide an essential structural basis for understanding copper homeostasis in living cells.